As a related art developing device, for example, JP-A-10-240008 describes a process cartridge, in which a development roller and a developer cartridge are housed in a casing, and the developer cartridge is detachable with respect to the casing.
The casing includes a drive shaft member for receiving a driving force from a motor or the like. An agitation part for agitating developer in the interior of the developer cartridge is accommodated in the developer cartridge, and an engaging recess is provided in an end portion of a rotating shaft of the agitation part. When the developer cartridge is attached to the casing, the drive shaft member is fitted in and coupled with the engaging recess, and the driving force is transmitted from the drive shaft member to the agitation part.
The above described related art developer cartridge has some disadvantages. For example, if gear teeth are formed on each of the drive shaft member and the engaging recess, and as their gear teeth mesh, the drive shaft member is coupled with the engaging recess.
In that case, when the developer cartridge is installed to the casing, there is a possibility that tips of the gear teeth of the drive shaft member and tips of the gear teeth of the engaging recess collide against each other in the course of the installation. In that case, since the gear teeth of the drive shaft member and the gear teeth of the engaging recess become unable to mesh, it becomes difficult to smoothly install the developer cartridge to the casing. Thus, the tips of the respective gear teeth of the drive shaft member and the engaging recess can be damaged.